Abstract
Purpose::
Dopamine (DA), nitric oxide (NO) and retinoic acid (RA) are known to adjust retinal function to varying levels of ambient illumination. We have previously presented evidence supporting the role of retinoic acid in turtle retina and its interactions with nitric oxide. Here, we tested the interactions between the three neuromodulators: DA, NO and RA.
Methods::
Intracellular recordings from L1-horizontal cells in the turtle eyecup preparation. Response-intensity curves (V-LogI) were measured in the dark-adapted state during superfusion with control solution and with different mixtures of the three neuromodulators and related drugs (dopamine, haloperidol, all-trans retinoic acid, l-arginine and L-NAME). The maximum response amplitude (Vmax) was used to assess the effects of the experimental solutions.
Results::
RA-induced reduction of Vmax was augmented by L-arginine (increased NO), and reduced by L-NAME (decreased NO). NO augmentation of Vmax and RA diminution of Vmax were not affected by exogenous application of dopamine or haloperidol. Neither dopamine nor haloperidol alone caused any change in the V-LogI curves of turtle L1-horizontal cells.
Conclusions::
Retinoic acid acts as an NO-dependent neuromodulator, while the actions of both retinoic acid and nitric oxide appear to be independent of the dopaminergic system.
Keywords: retina: distal (photoreceptors, horizontal cells, bipolar cells) • retinal connections, networks, circuitry • neurotransmitters/neurotransmitter systems